As a general model of a conventional bent pipe and a manufacturing method of the bent pipe, a rubber radiator hose which is formed in the shape of a bent pipe by a mandrel will be explained with reference to FIGS. 14 to 16. FIG. 14 is a plan view of a hose 110 having an intermediate portion bent approximately 90°. This hose 110 is provided with a bent portion 120 in a middle portion thereof and straight portions 130 and 132 connected to each side of the bent portion 120 in the longitudinal direction thereof.
In this example, the bent portion 120 and the straight portions 130, 132 are formed in a perfect circle shape in rotational cross section having an inner diameter D respectively as indicated by (a) and (b) in the drawing, and the bent portion 120 is formed in a curved round shape bent approximately 90°. In addition, a cross section indicated by (c) in the drawing corresponds to a cross section of a bent portion having a horizontally long elliptical shape (horizontally long flat shape), which is disclosed in a Patent Reference 1, discussed below.
Herein, various terminology used in this application will be explained. A circle having a curvature of a circular arc forming a round shape portion is a round circle C, a center of this round circle C is a round center CO, and a radius of the round circle C is a round radius CR. A numerical value of the round radius is a value of a round indicating a size of the round shape portion. For example, in the case where the round radius is 40 mm, a round of the round shape portion is 40 and is expressed as R40. It is noted that when the round radius CR is small, the curvature of the round shape portion is large, and the curvature of the round shape portion increases with decrease in the round radius CR.
Moreover, a center axis of the hose is HC, and a point on the center axis HC is a hose center HO. A cross section of the hose taken in an orthogonal direction of the center axis HC is a transverse cross section, in which a cross section of the bent portion taken in the radial direction of the round is a cross section in the radial direction of the round (the round radius direction).
Further, a condition of the hose shown from a direction orthogonal to the round circle C is a plan view. In this plan view, a side of the round center CO of the bent portion is an inside and an opposite side is an outside. An outer circumferential surface of the hole located between the inside and the outside is a lateral surface.
Furthermore, in the cross section in the radial direction of the round, the direction of the round radius is a vertical direction, and the direction orthogonal to the vertical direction is a horizontal direction. In a cross sectional shape in the radial direction of the round, a shape having different lengths in the vertical direction and in the horizontal direction passing the hose center HO is a flat shape. In particular, the shape of which the length in the horizontal direction is larger than that in the vertical direction is a horizontally long flat shape, while the shape of which the length in the vertical direction is larger than that in the horizontal direction is a vertically long flat shape.
Still further, a straight line passing the round center CO and the hose center HC is a center line L1 in the vertical direction, and a straight line which is orthogonal to the center line L1 in the vertical direction and passes the hose center HO is a center line L2 in the horizontal direction (see FIG. 2).
Like reference characters shall be commonly used in embodiments to referred to later.
In addition, in the description with reference to the drawings, the orientation such as upward, downward, left, right and the like shall be designated based on each direction such as upward, downward, left, right and the like in the drawings referred to in the description.
FIG. 15 shows a cross section of the bent portion 120 at the time of finishing a vulcanizing molding. The hose 110 is formed in the same bent shape as a mandrel 140 by putting an unvulcanized hose on the mandrel 140 which has the same bent shape as the hose 110, and vulcanizing it by heating it at a predetermined temperature.
At that time, a bent portion 142 of the mandrel 140 has substantially the same curvature as an inner circumferential portion of the bent portion 120. In the case where a round of an inner round portion 144 of the bent portion 142 is sharp to some extent, an inner round portion 124 of the bent portion 120 is separated from the inner round portion 144 of the mandrel 140 when the unvulcanized hose is put on the mandrel 140, and a space 180 is formed between the inner round portion 124 and the inner round portion 144.
Then, since the inner round portion 124 is compressed toward the center in the longitudinal direction as indicated by an arrow f1, the inner round portion 124 is subjected to buckling deformation toward an inside of the space 180 by compression force in the direction of arrow f1. Due to this buckling deformation, a poor appearance part 190 formed in an irregular shape, such as wrinkles or the like, is easily produced.
The reason why the space 180 is formed is because the inner round portion 124 is subjected to a restoring force in the direction of arrow f3 which is separated from the inner round portion 144 of the mandrel and directed to the round center CO, due to its own restoration elasticity by bending, and by this restoring force, the inner round portion 124 has a tendency to be separated apart from the inner round portion 144 of the mandrel. At that time, since the restoring force increases with a decrease in round of the inner round portion 124, the space 180 is easy to be formed.
In addition, an outer round portion 126 of the bent portion 120 is pulled in the directions indicated by arrows f2 and comes into tight contact with an outer round portion of the mandrel. Therefore, the poor appearance part 190 may not be formed, or only minimally formed, on the outside.
Further, there is another example in which, in order to suppress the creation of the poor appearance part 190 on the inside of the bent portion, the bent portion is formed in a horizontally long flat shape (see FIG. 14(c)) and a circumferential length of an inner circumference of the hose is gradually increased (see the Patent Reference 1) in the longitudinal direction of the hose.